The Government could face more legal action over air pollution after environmental lawyers warned its new air quality plan is not good enough.

The long-awaited plan focuses on bringing in clean air zones in five English cities by 2020 which will use charging to discourage the most polluting vehicles, including old diesel buses, taxis, coaches and lorries, from entering the city centres.

They will be introduced in Birmingham, Leeds, Nottingham, Derby and Southampton by the end of the decade but will not affect private cars.

Environment Secretary Elizabeth Truss said: " Our clean air zones are targeted on the largest vehicles, whilst not affecting car owners and minimising the impact on business.

"We want to ensure people can continue to drive into city centres and by targeting action at the most polluting coaches, taxis, buses and lorries we will encourage the use of cleaner vehicles."

Ministers were ordered by the Supreme Court earlier this year to produce plans to comply with European Union law on limits for nitrogen dioxide in the air.

The ruling was the culmination of a five-year legal battle by environmental group ClientEarth over the UK's ''admitted and continuing'' failure to comply in certain zones with limits set under the Air Quality Directive ''for the protection of human health''.

Nitrogen dioxide air pollution, including from vehicles, causes about 23,500 early deaths a year in the UK, with pollutants known as particulate matter which come from many of the same sources also responsible for thousands of premature deaths.

Responding to the new plan, ClientEarth air quality lawyer Alan Andrews, said: "In April, the Supreme Court ordered the Government to come up with a plan to achieve legal pollution limits as soon as possible.

"The Government's latest plan for clean air zones doesn't tackle pollution from passenger cars - one of the biggest sources of pollution - and ignores the problem in dozens of other cities where people are breathing illegal levels of pollution."

He added: "We need to study these plans in detail but on first glance they don't seem to achieve air quality standards we want to see, as soon as possible.

"If on further examination we are not fully satisfied, and we believe that thousands more lives will be put at risk, then we will take the Government back to court in the new year."